Increasing aerodynamic efficiency is an important factor to be considered in commercial aircraft design. To this end a number of devices may be incorporated at the tip of wings, such as winglets, raked-tip devices, wing tip fences and planar wing extensions. Such wing tip devices are provided for purposes such as reducing the strength of the wing tip vortex, moving the wing tip vortex away from the fuselage, and/or increasing the upward lift over the tip portion of the wing.
Whilst improving aerodynamic efficiency, wing tip devices may lead, particularly during high-load conditions, to greater aerodynamic loads on the wing and therefore greater bending moments in the wing. (High-load conditions may occur during, for example, turbulence or a sharp turn.) The maximum bending moment to which a wing is expected to be subjected during its lifetime is likely to dictate the required strength of the wing. This in turn may dictate the weight of the wing. Thus, the gains in aerodynamic efficiency attained by adding a wing tip device have, in aircraft designs of the prior art, been offset by an increase in the structural mass of the aircraft required to cope with the increased wing loading.
It is an object of the present invention to provide an aircraft that is able to benefit from the improved aerodynamic efficiency that can be achieved through the provision of a wing tip device, whilst mitigating the problems associated with the increase in structural mass suffered by the above-mentioned prior art.